Media storage systems are well-known in the art and are commonly used to store data cartridges at known locations and to retrieve the desired data cartridges so that data may be written to and/or read from the data cartridges. Such media storage systems are often referred to as autochangers or library storage systems.
A typical autochanger or media storage system may include one or more different types of cartridge-receiving devices. For example, one type of cartridge-receiving device may comprise an individual cartridge storage location (e.g., for holding a single data cartridge) or a storage rack or “magazine” (e.g., for holding a plurality of data cartridges). Another type of cartridge-receiving device may comprise one or more cartridge read/write devices for reading data from and/or writing data to data cartridges. Yet another type of cartridge-receiving device is a cartridge-engaging assembly or “picker.” The cartridge-engaging assembly is provided for transporting the data cartridges in the media storage system (e.g., between the storage magazines and the read/write device).
In operation, it is often useful to know whether a data cartridge is present in any of the various cartridge-receiving devices. At start-up, for example, it may be necessary to know whether there is already a data cartridge in the cartridge-engaging assembly which should be returned to a storage magazine before the media storage system will be ready for service.
One way to determine whether a data cartridge is present in a cartridge-receiving device is by monitoring mechanical switches. When a data cartridge passes into or out of the cartridge-receiving device, a switch is thrown (e.g., turned “on” or “off”) to indicate the presence or absence of the data cartridge. However, mechanical switches have finite tolerances; a smaller data cartridge may pass into or out of the cartridge-receiving device undetected. This especially occurs if different sizes of data cartridges are to be used in the same media storage system.
It may also be useful to know which size data cartridge is present in the cartridge-receiving device. For example, if a smaller linear tape open (LTO) data cartridge is being retrieved for a read/write operation, it may be necessary to deliver the data cartridge to a read/write device designed for smaller LTO data cartridges. Alternatively, if a larger digital linear tape (DLT) data cartridge is being retrieved for a read/write operation, it may be necessary to deliver the data cartridge to a different read/write device designed for larger DLT data cartridges. Current approaches rely on separation of the different types and sizes of media into physically different media storage systems.